An electromagnetic wave is described as which of the following?

• A. A type of wave that requires a medium to travel
• B. A type of wave, such as a light wave or radio wave, that does not require a medium to travel
• C. A longitudinal wave that transfers energy
• D. A wave that only travels in air

Answer: (B)

Electromagnetic waves can travel without a medium because they are self-sustaining oscillations of electric and magnetic fields that support each other. They are transverse waves, with the electric and magnetic fields oscillating perpendicular to the direction of travel, which allows propagation through vacuum as well as through various media. This is why sunlight and radio waves can reach us through space. Mechanical waves, by contrast, rely on a medium to carry energy; they involve the motion of particles in the medium. The idea that an electromagnetic wave is longitudinal or that it travels only in air is incorrect, because electromagnetic waves have transverse oscillations and can propagate through vacuum.